Everyone wonders how the zebra got its stripes, but no one asks how it lost them.
The answer lies not in an ancient myth or even in a childhood fable, but within the collections of the Yale Peabody Museum.
By extracting ancient DNA from the now extinct quagga, professor of ecology and evolutionary biology Adalgisa Caccone and her team were able to tie this animal to the plains zebra of South Africa. Their findings indicate that the genetic make-up of the zebra and the quagga are strikingly similar and may connect as far back as 6,000 years. The study has recently been printed in the Sept. 22 issue of the British journal Biology Letters.
Studies on the DNA of the quagga began 20 years ago, but only recently has there been significant progress in the use of ancient DNA samples.
“20 years ago, the field of ancient DNA started with a paper on the quagga,” Caccone said. “We wanted to revisit the paper because there has been a lot of progress since that time.”
Physically, the quagga appears to be a zebra in the midst of losing its stripes with the markings extending to its mid-torso, then blending into a solid brown. Scientists predict that it evolved when a population of the plains zebra was isolated during the ice age. Thus, the divergence from the typical appearance of the zebra is not unusual considering the increased biodiversity brought about by the Ice Age.
The quagga survived this period and continued to exist through the 1800s. It even lived long enough to be photographed.
“Our species is a mare from the London Zoo, and she is the only quagga photographed from life,” Zyskowski said.
This means that the now-extinct quagga species, believed to have evolved from the plains zebra, lived for 120-129,000 years before dying off.
Scientists are now able to obtain DNA from minute fragments of tissue, which are amplified and sequenced in order to map a species. Caccone likens this method to that of forensics, in which only a hair or a small drop of blood is needed to make an investigation.
“The beauty is to be able to analyze, at a genetic level, both extinct and extant animals using the same tool, which is DNA,” Caccone said.
The team extracted a bone sample from the Peabody’s quagga skeleton, which is the only known complete quagga skeleton, using a controversial process known as destructive sampling. A sample of the skin of the same quagga, which is located in The Edinburgh Museum in Scotland, was also extracted in the same manner.
This method is controversial because it permanently changes the specimen, but Kristof Zyskowski, the collection manager of vertebrates at the Peabody Museum, said these means were worth the ends.
“I believe that destructive sampling, if well justified, can be and even should be done if any progress in science is to be made,” Zyskowski said.
Dorcas MacClintock, a veteran of the equine field and author of “A Natural History of Zebras,” said he has taken great interest in the recent discovery correlating the quagga with the contemporary plains zebra.
“I think [the quagga] is a fascinating animal, because it is the southern-most representative of the plains zebra,” said MacClintock, who published an article detailing the Peabody’s acquisition of the quagga two decades ago.
Although there are 23 quagga specimens in the world, they are all spread out among institutions throughout the world, she said.
Caccone said she sees this separation as a benefit for scientists.
“It forces communication and collaboration between labs, [and] it’s fun to do because you have to be very open about your results,” she said.
Zyskowski said the logical extreme of this philosophy is the notion of a “world museum” in which members of the scientific community allow access to appropriate specimens.